The present invention relates generally to digitizing panels, and more particularly to a method and apparatus for managing power consumption of a digitizing panel.
Digitizing panels having a resistive layer covered with a non-conductive plate such as glass, are known in the art. The known digitizing panels may operate in one of two modes, namely a touch mode or a pen mode. When operating in the touch mode, a computer is conventionally configured so as to capacitively bias the resistive layer by applying to a shield layer of the digitizing panel an AC signal. An object such as a user's finger that approaches and contacts the non-conductive plate acts as a load that is capacitively coupled to the resistive layer. The capacitively coupled load causes electric current to flow through the corners of the resistive layer. The computer may determine a Cartesian coordinate (X, Y) position of an object relative to the digitizing panel, based on the current flow in each of the corners of the resistive layer in a manner known to one of ordinary skill in the art. More particularly, the position of the pen relative to the digitizing panel may be determined based upon a ratio of the corner currents or signals that flow through the corners of the resistive layer due to the object being capacitively coupled to the resistive layer.
When operating in the pen mode, the computer is conventionally configured so as to be receptive to a signal transmitted from a hand-held stylus or pen. In particular, a pen typically includes a battery portion which supplies power to an oscillator portion for stimulating a coil associated with a transmitter portion to transmit an AC signal from a tip of the pen. The AC signal may be transmitted from the pen tip when the tip contacts an object or surface such as the non-conductive plate associated with the digitizing panel.
The transmitted AC signal is typically capacitively coupled to the resistive layer associated with the digitizing panel. The capacitively coupled AC signal induces an electric current flow through each of the corners of the resistive layer. As in the touch mode, the position of the pen relative to the digitizing panel may then be determined based upon a ratio of the corner currents or signals that flow through the corners of the resistive layer due to the AC signal transmitted from the pen.
Therefore, these digitizing panels must bias the resistive layer with an AC signal in order to detect a touch but need not bias the resistive layer with an AC signal in order to detect a pen because the pen transmits an AC signal to the resistive layer. Furthermore, more hardware is required to detect a touch than to detect a pen due to the signal characteristics of the currents that flow through the corners of the resistive layer in response to pen contact and the signal characteristics of the currents that flow through the corners of the resistive layer in response to a touch. This biasing of the resistive layer and the powering of the additional hardware to detect a touch consumes power.
However, reducing power consumption in portable computers has gained a great deal of attention in the technical community as a result of a set of conflicting user requirements and technological constraints. On the one hand, users would like to operate these portable devices for extended periods of time without access to an AC wall outlet. This means that such devices must carry their own power sources, i.e., batteries of various types. On the other hand, the total energy stored in such batteries varies almost directly in proportion to their weight. Carrying heavy batteries of course, detracts from the portability of these machines.
These power consumption issues are of particular concern to digitizing panels since digitizing panels are a viable input alternative for the mouse and keyboard of portable computers. What is needed therefore is a method and an apparatus for managing power consumption of a digitizing panel.